Iron deficiency is a serious public health problem in resource-poor areas of the world, yet little is known at the molecular level regarding the cellular adaptation to iron deficiency. We performed microarray analyses in S. cerevisiae which revealed that multiple metabolic pathways are regulated in response to iron availability. Notably, several proteins and pathways containing iron-sulfur cluster enzymes are down-regulated in yeast grown in iron-poor media. These transcriptional changes suggested that changing iron levels may alter the flux of metabolites through these pathways. We have performed metabolite analyses on yeast grown under conditions of iron deficiency and found that amino acid biosynthesis, lipid synthesis, and carbon metabolism are all affected by iron deficiency.[unreadable] In some yeast species, such as Pichia guillermondii, the biosynthesis of riboflavin is activated in response to iron deficiency. In collaboration with the laboratory of Yuriy Boretsky at the Institute of Cell Biology, NAS, Ukraine, we are developing tools to study gene function in this industrially important yeast, and we have mutant strains of Pichia that exhibit misregulation of iron uptake and riboflavin biosynthesis.